Professor Hammer’s Metalworking Tips - July 2013

Q. Hi Ron, I have a lot of your DVDs, and have asked you many questions online. Here's another one: Is it possible to cut 18- or 20-gauge sheetmetal with hand shears? I don't mean just trimming an edge, but to cut a 2-foot square piece in half, and not with tin snips, but with aviation shears. I am on blood thinners and would like to avoid wounds to the hands! What is the secret?

Ed Barras
Via the Internet

A. It's really not very feasible to cut through the middle of a sheet of 18-gauge steel with the "standard" type of aircraft shears, but here's a way it can be done:

Draw two lines across the panel, about ¾ inch apart, where you want the cut to go. Assuming you like to cut with the handles of the shears above the metal, start with the red-handled shears, and cut in about 1 inch on the right-hand line. Now, with the green-handled shears, cut on the left-hand line, and go in as far as you can, probably about 1½ inches. Now, go back to the right side with the red shears, to about 2 inches, and alternate back and forth in that manner.

2/2You can cut cleanly through the center of a piece of metal by removing a narrow strip with left and right aircraft shears.

Working in this way, you'll be removing a strip of metal between the two lines, and the cutting action of the shears will peel this strip up above the sheet you're cutting. If you're using the shears correctly, you will get very little distortion on the base panel, no matter how far into the panel you cut – all distortion will go into the “waste” piece. If you like to cut with the handles of the shears below the metal, just reverse everything.

The very best gloves for preventing cuts are made of Kevlar, which is nearly impossible to cut with sharp metal edges. I prefer wearing lighter gloves, which give me better feel, but they don't offer the same protection.

Q. I have a 1954 Effie that my dad and I are rebuilding. It needed lower door skins, and we've welded those in place, but one of the door's outer skins apparently shrunk from a bit too much heat. The second panel didn't do this, but we took much longer to put it together, allowing more cooling time. Can you tell me how I can reverse the problem? It will pop out by hand, but as soon as pressure is released, it drops back in.

Mike Conner
Via the Internet

A. The problems you have are almost certainly caused by shrinking at the joint caused by the heat of welding. The fix is to stretch the weld, and this is normally done by hammering on-dolly on the weld, and/or on the metal adjacent to the weld. While this sounds simple, it seldom is. If the weld was made with a TIG or gas welding outfit, it's not too hard to hammer on the weld, since these welds are relatively soft. If we're talking about a MIG weld, this is distinctly harder, and only a limited amount of hammering on the weld is possible, although the metal next to the weld can usually be hammered. I presume you know that the weld should be ground flat on the outside before hammering. Be sure to prevent the metal from overheating when you grind the weld. If the grinding heats the metal enough to cause a color change, that can cause problems too.

Nevertheless, on large, low-crown panels such as a door skin, just a tiny bit of excessive stretching or shrinking will cause the “oil-can” situation you are describing, and it takes a lot of delicate control of these processes to get everything to “relax” and be stable in the shape you're trying to achieve. I encourage you to do your best to straighten what you've got, but don't be afraid to go to someone with more experience if it seems to be getting worse rather than better!

You can email your questions to Professor Hammer at covell@cruzio.com, or mail to Professor Hammer, c/o CLASSIC TRUCKS Magazine, 1733 Alton Pkwy., Irvine, CA 92606. You'll receive a personal reply! We'll print your name and city unless you request otherwise. Ron Covell has made many DVDs on metalworking processes, and he offers an ongoing series of workshops across the nation covering all aspects of metalworking. Check them out online at www.covell.biz, or call for a current schedule of workshops and their free catalog of DVDs. Phone 800-747-4631, or 831-768-0705. You can send a request by mail to: Covell Creative Metalworking, 106 Airport Blvd. #105, Freedom, CA 95019.